Electromagnetic follow-up observations of the gravitational wave-detected binary neutron star merger (NSM) GW1701817 suggested that material ejected from the accretion disk formed in the merger underwent a robust r-process nucleosynthesis, producing heavy elements like Au, Pt, and Eu. These observations seemed to answer a long-standing question about the origin of the heaviest elements in the Universe. However, the conditions that characterize the disks formed in NSMs are also found in other systems, raising the question of whether mergers are unique sites of r-process production. Of particular interest for this question is the collapse of rapidly-rotating massive stars, called "collapsars." Like NSMs, collapsars form accretion disks around stellar mass compact objects and are associated with ultrarelativistic outflows that give rise to gamma-ray bursts, similarities that suggest they may also host an r-process. I will review the theoretical progress that allowed the identification of the emission accompanying GW170817 as a specifically r-process-powered transient. I will then discuss recent work that explores whether collapsar disks could successfully produce the r-process, and what the signs of collapsar disk r-process nucleosynthesis might be. I will conclude by highlighting upcoming advances that will allow us to make progress on understanding of r-process origins and other mysteries of the multi-messenger era.